What source are you selecting? Is it the Kodak i30 or something else like Kofax VirtualReScan?
If it is something else it is possible that the other source doesn’t have a way to know that the scanner doesn’t have any paper in the feeder. In those situations all that can be done is to return “-1” and then generate an error when the next Transfer is initiated.
Are you checking for an error when the Transfer is initiated?
Brian